With all the talk about the Swim Smart Initiative and the new swim starts at various NA WTC 140.6 events, I took a Go Pro video of the entire start at IMLP 2013 from the top of the boat house. Here's the video and my thoughts about how well it went from my view:

Yes you cross a timing mat, and as fast as you see that group in the video moving forward is as fast as you enter the water. It is very similar to a running race, everyone just shuffles forward until they cross the start line. And once you cross you can run out a bit and just start swimming. It is not very crowded unless you try to hug the buoys. The turns were moderately crowded on the first loop.

Couldn't see much on the video. Do people cross a timing mat as they enter the water? How many enter the water at a time?

I'd say about 15-20 get into the water at a time to start swimming. IMCDA was this way this year and I wasn't crowded at all except at the turns. The start was very relaxing. Like getting into the water with 10-15 of your friends and start swimming type of thing. I was passing people constantly which was a mental satisfaction sort of thing since I was very confident swimming.